Phase structures, morphologies, and NO catalytic oxidation activities of single-phase MnO2 catalysts

Abstract

The NO catalytic oxidation activities of single-phase α-, β-, γ-, and δ-MnO2 were investigated. All the catalysts were systematically characterized using various techniques. The results showed that the catalytic activities were significantly affected by the MnO2 phase structures. Among the four catalysts, the urchin-like γ-MnO2 showed the best NO catalytic oxidation activity across the studied temperature range, with the largest NO conversion, namely 88%, at 280°C. This is good activity, even compared with those of noble-metal-based catalysts. It also displayed the best activity during long reaction times. The NO catalytic oxidation activities of the other three catalysts decreased in the order α->β->δ-MnO2. The various phase structures of MnO2 contain the same [MnO6] octahedral units, but with different linking modes. γ-MnO2 has a disordered structure, resulting in larger numbers of active oxygen species, leading to a better catalytic performance.